Experiments that address the mechanisms of immunosuppressive action mediated by cyclosporine on human T lymphocytes are described in this proposal. To accomplish this goal, we shall examine both the immediate and long-term consequences of cyclosporine exposure on a heterogeneous panel of human influenza virus-specific and Epstein-Barrvirus-specific T cell clones. Clones are particularly advantageous for this study because they are homogeneous populations that are likely to produce clear-cut reuslts, because their immunologic characteristics are well-defined, and because their growth is regulated by antigen and achieved by a well-characterized hormonal system. Moreover, use of a panel of clones with different attributes will provide a depth of understanding for this analysis. Since cyclosporine apears to inhibit T cell activity by preventing the expansion of the cells after stimulation by antigen, assessment of the drug's effect on the clones will emphasize consequences on proliferation. Thus, thymidine incorporation will be measured after antigenic stimulation, mitogen activation, phorbol ester exposure, and anti-T3 monoclonal antibody incubation. Moreover, the effect of cyclosporine on pertinent lymphokine secretion (interleukin 2 and gamma interferon) as well as on pertinent T cell surface structures (Tac, Ia, transferrin receptor, T3, T4, and T8) will be determined in order to express immunosuppression mediated by the drug in terms of these parameters. Because the clones will be grown for long periods of time in continuous cultures, it will be possible to investigate the long-term effect of cyclosporine on T cells by periodically monitoring these lines for changes in functional or phenotypic characteristics. Related to this point, prolonged exposure of the clones to cyclosporine could result in resistant lines. Resistant clones will be sought by selection in the presence of the drug or by adaptation to gradually increasing concentrations of cyclosporine in the culture medium. Since cyclosporine is being used clinically for immunosuppression, a more complete understanding of its mechanism of action on human T lymphocytes in vitro could well provide rational guidelines for future therapeutic use of the drug. These studies on viral-specific T cell immunity are particularly interesting because of the clinical effects of immunosuppression and because previous studies have focused on the effect of cyclosporine on allogenic and mitogenic responses instead of virus-specific stimulation.